Movable safety tunnel for use during bridge maintenance

ABSTRACT

A movable safety tunnel rides on parapets within a bridge. The safety tunnel is locked in place in a respective section of the bridge while maintenance or other operations are performed on that section of the bridge. This allows the traffic to flow through the safety tunnel and along the bridge, and the safety tunnel shields the traffic from any dust or debris. When the maintenance on that respective section of the bridge has been completed, the safety tunnel is unlocked and pushed (and/or pulled) by suitable equipment to the next adjacent section of the bridge; and the safety tunnel is again locked in place as the maintenance is performed. This procedure continues, progressively, along the bridge. In one embodiment, the safety tunnel has a trolley system riding on respective rails constructed on top of the parapets.

FIELD OF THE INVENTION

The present invention relates to a movable shield and containment systemfor the maintenance of existing bridges and, more particularly, to a“safety tunnel” which is movable with respect to the bridge structure tofacilitate traffic flow along the roadway of the bridge (and/or underthe bridge) while protecting the traffic flow from falling debris duringthe maintenance work on the bridge.

BACKGROUND OF THE INVENTION

Existing bridges require substantial maintenance. The maintenance isrequired at least periodically, if not continuously. For example, it isoften necessary to remove the paint (such as a lead-based paint) fromthe steel structure of a bridge prior to applying a new coating thereto.To remove the paint, conventional sand-blasting or shot-blastingequipment is used. Suitable available measures are taken (as hereinafterdiscussed) to prevent the debris from falling onto the roadway, or intoany water below the bridge, or otherwise polluting the environment.

At the same time, it is also very desirable to facilitate the continuoustraffic flow along the roadway, while the maintenance is beingperformed, and thus avoid a complete shutdown of the traffic flow. Whilethe traffic flow is primarily vehicular or railway traffic, it is alsodesirable to maintain any pedestrian traffic as well as facilitateaccess for the maintenance crews. By maintenance, it is understood thatany repair or construction on the bridge is contemplated herein.

To maintain the traffic flow while the maintenance is being performed,the prior art has resorted to the use of a shield and containmentstructure (commonly referred to as a “traffic shield”) constructedwithin or under the bridge, along a given length thereof, and above thedeck or roadway of the bridge.

This conventional traffic shield, together with the roadway, provides acomplete enclosure for the traffic flow (which may be vehicular,railway, pedestrian or some combination thereof). Within the trafficshield (or thereunder) the traffic is protected against any fallingdebris—such as paint chips from the bridge, the materials of shotblasting or sand blasting, and any tools, components or structuralelements accidentally dropped by the maintenance workers. By the sametoken, the workers are protected against the vehicular or rail traffic.As a result, a complete shut-down of the bridge is avoided, and thetraffic flow is substantially unimpeded while the maintenance is beingperformed.

However, when the maintenance has been completed on a given length orsection of the bridge, the traffic may be halted for a substantialperiod of time sufficient to enable the workers to completely dismantlethe traffic shield, move its individual components to the nextsuccessive section of the bridge, and then re-assemble the trafficshield therein. This is time-consuming, hence expensive, and causes asubstantial traffic problem; and a need exists for a more efficientsolution to this long-standing problem.

BRIEF SUMMARY OF THE INVENTION

Accordingly, it is the primary object of the present invention toalleviate the disadvantages and deficiencies of the prior art byproviding a movable safety tunnel within the bridge, thereby resultingin a substantial cost-savings and, concurrently, holding theinconvenience to the motorists to an absolute minimum.

The present invention finds particularly utility for use in connectionwith a bridge having a roadway for vehicular and/or pedestrian traffic,wherein maintenance is being performed on the bridge, and wherein asafety tunnel is constructed within a respective longitudinal section ofthe bridge. Accordingly, the traffic flows on the roadway of the bridgesubstantially uninterrupted while the maintenance is being performed onthe respective longitudinal section of the bridge. More specifically,the traffic on the roadway of the bridge is protected against fallingdebris, such as paint particles, materials for shot blasting orsandblasting, tools, components and the like. At the same time, theworkers performing the maintenance are shielded from the traffic flow.Once the maintenance on the respective longitudinal section of thebridge is completed, the traffic shield is normally dismantled andthereafter reconstructed on a next adjacent longitudinal section of thebridge.

In the improvement of the present invention, the traffic shieldcomprises a safety tunnel which is movable along the length of thebridge.

As a result, the necessity for repeatedly dismantling and reconstructinga conventional traffic shield is eliminated (as the maintenance on thebridge progresses along the length of the bridge).

For example, and in comparison to the prior art, if the bridge issixteen hundred (1600) feet long, and if the conventional traffic shieldis one hundred (100) feet long, it will have to be assembled,disassembled and re-assembled approximately sixteen (16) times. Thus istime-consuming and expensive and a distinct inconvenience, repeatedly,for the vehicular traffic on the bridge. With the present invention,however, the safety tunnel may be rolled from place to place along thebridge without requiring the safety tunnel to be taken apart.

In a preferred embodiment of the present invention, rails areconstructed on top of the respective parapets running along therespective sides of the deck or roadway of the bridge, and the movablesafety tunnel has a trolley system riding on the rails.

The trolley system is locked to a respective longitudinal section of therails as the maintenance is being performed on a correspondingrespective length of the bridge; and the trolley system is unlocked fromthe respective longitudinal section of the rails to enable the safetytunnel to be moved to the next adjacent section of the bridge on whichthe maintenance is to be performed. The safety tunnel is pushed and/orpulled by a tow truck (or other suitable piece of equipment) to the nextadjacent section of the bridge.

Preferably, the trolley system comprises a plurality of respectivespaced-apart trolley assemblies.

In the preferred embodiment, the safety tunnel includes an invertedU-shaped structure having a roof assembly joined to respective sidesdepending therefrom. These respective sides have lower portions carriedby the plurality of trolley assemblies riding on the respective rails.

These and other objects of the present invention will become apparentfrom a reading of the following specification taken in conjunction withthe enclosed drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-5 illustrate, schematically, the teachings of the prior art andthe disadvantages and deficiencies therein.

FIG. 1 is a schematic (pictorial) side elevation of a typical bridgeusing a stationary traffic shield—heretofore habitually resorted to inthe prior art—to facilitate vehicular traffic flow during maintenanceoperations on a selected section along the length of the bridge.

FIG. 2 is a cross-sectional view thereof, taken along the lines 2—2 ofFIG. 1 and drawn to an enlarged scale.

FIG. 3 corresponds substantially to FIG. 1, but shows the prior artstationary traffic shield being dismantled following completion of themaintenance on the respective lengthwise section of the bridge.

FIG. 4 corresponds substantially to FIG. 3, but shows the traffic shieldbeing re-assembled on the next adjacent lengthwise section of thebridge.

FIG. 5 corresponds substantially to FIG. 4, but shows the traffic shieldre-assembled and fixed in place to again resume flow of the vehiculartraffic.

FIGS. 6-9 illustrate, schematically, the improvement of the presentinvention and its features and advantages.

FIG. 6 corresponds substantially to FIG. 1; however, the traffic shieldis not fixed or stationary but, rather, constitutes a movable safetytunnel that may be moved along the length of the bridge as progressivesections of the bridge are being worked on and maintained.

FIG. 7 is a cross-sectional view thereof taken along the lines 7—7 ofFIG. 6, drawn to an enlarged scale and corresponding substantially toFIG. 2, and showing the movable safety tunnel having a trolley systemriding on rails replaceable mounted on top of the respective parapets atthe sides of the roadway—the trolley system being selectively locked andunlocked on the rails—such that the safety tunnel is movable into thenext adjacent section of the bridge.

FIG. 8 corresponds substantially to FIG. 6, but shows the safety tunnelbeing moved to the next adjacent section of the bridge.

FIG. 9 corresponds substantially to FIG. 8 but shows the safety tunnellocked in place on the next adjacent section of the bridge, therebyenabling the traffic flow to resume as the maintenance is performed onthe next adjacent section of the bridge.

FIG. 10 is a side elevation of the movable tunnel MT, the bridge beingshown schematically.

FIG. 11 is a portion of FIG. 10, drawn to an enlarged scale, and showingthe construction of the sides of the movable tunnel.

FIG. 12 is an end view of the movable tunnel which cooperates with theroadway of the bridge, the remainder of the bridge being omitted forease of illustration.

FIG. 13 is a portion of FIG. 12, drawn to an enlarged scale, and showingone of the trolley assemblies riding on a rail mounted on top of one ofthe parapets at each side of the roadway of the bridge.

FIG. 14 is an elevational view of a portion of one of the rails.

FIG. 15 is a top plan view thereof.

FIG. 16 is a bottom view thereof.

FIG. 17 is a plan view of one of the trolley assemblies within theoverall trolley system.

FIG. 18 is an elevational view thereof.

FIG. 19 is a cross-sectional view thereof, taken along the lines 19—19of FIG. 18 and drawn to an enlarged scale, and showing one of thetrolley assemblies.

FIG. 20 is a further cross-sectional view thereof, taken along the lines20—20 of FIG. 18 and drawn to an enlarged scale, and showing the J-boltsof the assembly in a locked position on the rail (the broken linesindicating the unlocked portion).

FIG. 21 is an elevational view of one of the J-bolts.

FIG. 22 is a front elevational view of one of the columns, the lowerportion of which is secured to the respective upstanding gusset platesof the trolley assembly.

FIG. 23 is a side elevational view of the column of FIG. 22.

FIG. 24 is an enlarged portion of the upper portion of the column shownin FIG. 23.

FIG. 25 is a top plan view thereof, taken along the lines 25—25 of FIG.24.

FIG. 26 is a side elevation of an end portion of the trolley assembly ofFIG. 18, drawn to an enlarged scale and detailed.

FIG. 27 is an end view thereof, taken along the lines 27—27 of FIG.26.

FIG. 28 is a side elevation of the other end of the trolley assembly ofFIG. 18 and, again, enlarged in scale and detailed.

FIG. 29 is a detailed view thereof, taken along the lines 29—29 of FIG.28.

FIG. 30 is a bottom view of the roof panel.

FIG. 31 is a longitudinal section view thereof, taken along the lines31—31 of FIG.30.

FIG. 32 is a detail view of one embodiment of the roof panel, drawn toan enlarged scale.

FIG. 33 is an end view of the one embodiment of the roof panel; thepanel is provided with connection tubes that fit inside the respectivecolumns.

FIG. 34 is a detail view of a second embodiment of the roof panel, drawnto an enlarged scale.

FIG. 35 is an end view of the second embodiment of the roof panel; andagain, the panel is provided with connection tubes that fit inside therespective columns.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIGS. 1-5, the disadvantages and deficiencies of theprior art will become readily apparent.

In FIG. 1, the workers W are performing maintenance, repair and/orconstruction operations on a given length L of a bridge B. While thiswork is being performed, the traffic flow of the vehicles isaccommodated by a conventional traffic shield T.

As shown in FIG. 2, the traffic shield T is an inverted U-shapedstructure which cooperates with the deck or roadway 14 of the bridge B.

In the prior art, the respective length L of the bridge B (being workedon) is enclosed by a suitable trap or cover C. This cover C is shownbroken away in FIGS. 1 and 5, and is omitted in FIG. 4 for ease ofillustration. The purpose of the cover C is to assure that the paintchips, the sand for sand-blasting or the steel balls used forshot-blasting, and any other dust and debris that is generated will bewholly confined within the cover C. A truck-mounted vacuum cleaner (notshown) continually removes all of the dust and debris; and whereshot-blasting equipment is used, filters out the steel balls forsubsequent reuse. Between the cover C and the bridge B, suitablecatwalks and/or scaffolding (also not shown) are installed forfacilitating the maintenance work and ready access for the workers.Again, all of this is well-known in the prior art; hence need not bedetailed herein.

Of significance, however, and as shown schematically in FIGS. 3 and 4,once the maintenance work on the respective length L of the bridge B hasbeen completed, the tunnel T must be completely dismantled ordisassembled, taken to the next adjacent length L′ of the bridge B, andre-assembled therein as shown in FIG. 5 to resume the normal trafficflow. The tunnel T, once assembled and installed within the length L (orL′) of the bridge B, is stationary and fixed in place. It is not readilymovable. Not only is the traffic flow interrupted for a substantial timeperiod, but excessive construction costs are incurred.

With reference to FIGS. 6-9, the improved tunnel MT of the presentinvention is movable, not stationary, and this is the key feature of theinvention.

The movable tunnel MT may be pre-fabricated in sections, taken to thebridge B and installed with use of a crane or other suitable equipment.Final assembly of the tunnel MT may take place on the bridge B. In apreferred embodiment, the tunnel MT may have length of around 200 feet.

The tunnel MT is movable along the entire length of the bridge (inprogressive increments) as the maintenance operations are performed. Forthis purpose, the tunnel MT has a trolley system (hereinafter describedin detail) which rides on specially-built rails on top of parapets oneach side of the roadway. When a particular section of the bridge B isto be worked on, the trolley system is locked against movement on therails; and when the work on that particular section of the bridge B hasbeen completed, the locking mechanism is released, and the entire tunnelMT (being movable as shown in FIG. 8) is pushed or pulled by a fork-lifttruck (or other suitable equipment) into the next adjacent, and possiblyoverlapping, position along the bridge B. Thereafter, and as shown inFIG. 9, the trolley system is again locked against movement of thetunnel MT along the length of the bridge B, so that the maintenance workcan be performed on the next section L′ of the bridge B; and the processis repeated until the work on the entire bridge B has been completed.

The movable tunnel MT is, of course, moved in the direction in which themaintenance is being performed on the bridge B.

With reference to FIGS. 10-12, the movable tunnel MT is an invertedU-shaped structure including a roof assembly 10 and a pair of parallelside wall assemblies 11 depending therefrom. The roof assembly 10includes a plurality of individual roof panels 12 connected torespective columns (hereinafter described) and each side assembly 11includes a plurality of individual side panels 13 connected torespective columns (hereinafter described) thus providing a modulardesign for construction of the complete movable tunnel MT. Preferably,the roof panels 12 and the side panels 13 are corrugated steel panels,as shown, but it will be understood by those skilled in the art that anysuitable panel, such as marine plywood, could be used if desired.

It will also be understood that the movable tunnel MT cooperates with anexisting deck or roadway 14 of the bridge B to provide a completeenclosure for the traffic flow.

With reference to FIGS. 12-21, the bridge roadway 14 has respectivebarrier walls or parapets 15 at each side thereof, and a rail 16 issecured to the top of each parapet 15. Each rail 16 is a closed tube (orbox) which, in a preferred embodiment, is 4×4×¼inches thick.Spaced-apart transverse flanges 17 are welded to the bottom of each rail16, and the flanges 17 extend laterally from the respective sides of therail 16, thereby assuring lateral stability of the rail 16 on theparapet 15.

These flanges 17 are spaced approximately four feet apart along thelength of the rail 16. A {fraction (13/16)}inch hole is drilled in eachflange 17 (and in each bottom wall of the rail 16) along the center lineof the rail 16. A 3¼inch access hole 18 is drilled in the top of therail 16 along the center line of the respective transverse flange 17. Asuitable concrete anchor bolt 19 passes through each access hole 18 andanchors the rail 16 to the parapet 15.

A trolley assembly 20 rides on each rail 16 (as shown more clearly inFIG. 20). This trolley assembly 20 has a wheel assembly 21 (see FIG. 19)rotatably journal ed in sintered oil-impregnated bronze bearings 22 on acentral axle or pin 23. These bearings 22 are more desirable thanball-bearings for a grit-laden or shot-laden environment. The respectiveends of the pin 23 are secured in a pair of downwardly-projectingspaced-apart channels 24 provided with stiffeners 25. These channels 24are part of a gusset assembly 26. A plurality of gusset assemblies 26are provided, being spaced approximately eight feet apart along thelength of the trolley assembly 20.

The wheel assembly 21, preferably, consists of a section of a 6⅝inchpipe 27 cut to a length of 4½inches and welded between a pair ofcircular side plates 28 and 29, respectively. The diameter of thesecircular side plates 28, 29 extends beyond the 6⅝inch O.D. of the pipe27, such that the radially-extending portions of the circular sideplates 28, 29 straddle the four-inch closed-channel rail 16, therebyproviding lateral stability of the trolley assembly 20 on the rail 16(even if high winds are encountered).

Each gusset assembly 26 has a pair of spaced-apart upwardly-extendinggusset plates 30, and each of the gusset plates 30 is provided with acentral transverse stiffener 31. Each gusset plate 30 further has a pairof spaced-apart {fraction (15/16)}inch holes 32, one on each side of thestiffener 31.

A plurality of columns 33 are provided. Each column 33 comprises arectangular tube 34 that is split on top and welded to a central plate35. A pair of angles 36 depend from the lower end of the column 33, andthe lower portion of each column 33 has a pair of spaced-apart {fraction(15/16)}inch holes 37.

These holes 37 on each column 33 align with the holes 32 on the gussetplates 30, thereby facilitating the bolting of the column 33 to thegusset assemblies 26 (and hence to the trolley assembly 20 which rideson the rail 16).

The roof assembly 10 is adjustable mounted to the top portions of therespective columns 33.

The roof assembly 10 has a plurality of depending members 38 telescopedwithin the columns 33, and each member 38 has a plurality of verticallyspaced-apart holes 39 aligned with corresponding holes 40 within the topportions of the respective column 33 for securing the members 38 (andhence the roof assembly 10) to the columns 33. The roof assembly 10consists of a plurality of corrugated horizontal panels 12, and the roofassembly 10 is raised or lowered on the columns 33 by suitable hydraulicjacks (not shown). This allows the roof assembly 10 to be lowered toclear the structural elements of the bridge B while rolling the movabletunnel MT into its next position along the bridge B. Once adjustedvertically, a drift pin (not shown) is inserted between the alignedholes 39 and 40, respectively.

The trolley assembly 20 is locked against the rails 16, so that themovable tunnel MT does not move while the work is being performed on theparticular portion of the bridge B. More specifically, each gussetassembly 26 has a pair of J-bolts 41 carrying respective nuts 42. EachJ-bolt 41 may be loosened and then rotated approximately 180° on itsaxis (see FIG. 20) such that a right-angularly bent portion 43 of eachJ-bolt 41 is received between the bottom of each rail 16 and itsrespective parapet 15. When the respective nuts 42 are tightened, theJ-bolts 41 are secured against the rail 16 and the trolley assemblies 20(and hence the movable tunnel MT) are locked against longitudinalmovement along the bridge B.

Suitable side panels 13, such as corrugated sheeting or marine plywoodpanels, are secured between the respective columns 33, therebycompleting the movable tunnel MT. This assures that no dust particles,shot blasting or sand blasting material or debris will enter into themovable tunnel MT, thereby protecting the traffic flow therein.

In the preferred embodiment of the present invention, the movable safetytunnel MT is one hundred and ninety-eight (198) feet long, and isdivided into six (6) sections, each of which is thirty-three (33) feetlong. Each section is raised by a crane and lifted in place. In onepractical application, the bridge B is over water; and the respectivesections of the safety tunnel MT are transported by a barge. One end ofeach section of the safety tunnel MT has a pair of tongues 44 (see FIG.26) which cooperate with a pair of plates 45 (see FIG. 27). Holes 46 inthe tongues 44 are aligned with holes 47 in the plates 45, and a pin orbolt (not shown) is received in these aligned holes, thereby assemblingthe respective sections together to form the complete safety tunnel MT.

Moreover, in the practical application, the portion of bridge B beingmaintained is approximately eighteen hundred (1800) feet long. In thatapplication, the rails 16 are constructed along approximately fivehundred (500) feet at one end of that portion of the bridge B. When themaintenance work is completed on length L of the bridge B, the safetytunnel MT is moved to the remaining length of the rails 16 on the bridgeB, and then the rails 16 are taken up in a “leapfrog” fashion, sectionby section, and re-installed ahead of the safety tunnel MT and so onuntil the maintenance work on the complete length of the bridge B hasbeen completed. A fork lift truck (or other suitable equipment) movesthe safety tunnel MT into its next position.

Only one lane of the bridge B may be closed off to re-install the rail16.

All of the components and/or materials of the movable tunnel MT of thepresent invention are readily available on the market, and the assemblythereof is relatively quick and convenient. Moreover, it will beappreciated by those skilled in the art that the dimensions of thevarious components disclosed herein are not for purposes of limitationbut, rather, for purposes of making a complete disclosure to facilitatea review of the present invention by one skilled in the art and a readyappreciation of the features and advantages of the invention.

Obviously, many modifications may be made without departing from thebasic spirit of the present invention. Accordingly, it will beappreciated by those skilled in the art that within the scope of theappended claims, the invention may be practiced other than has beenspecifically described herein.

What is claimed is:
 1. In a bridge having a roadway for vehicular,railway and/or pedestrian traffic, the roadway having a usable givenwidth for normal traffic flow, wherein maintenance, repair orconstruction operations are being performed on the bridge, and wherein atraffic shield is constructed within a respective longitudinal sectionof the bridge, thereby enabling the traffic to flow on the roadway ofthe bridge substantially uninterrupted while the maintenance, repair orconstruction operations are being performed on the respectivelongitudinal section of the bridge, such that the traffic on the roadwayof the bridge is protected against falling debris, and, at the sametime, the workers performing the maintenance, repair or constructionoperations are shielded from the traffic flow, and wherein when theoperations on the respective longitudinal section of the bridge arecompleted, the traffic shield is normally dismantled and thereafterreconstructed on a next adjacent longitudinal section of the bridge, theimprovement wherein the traffic shield comprises a safety tunnel whichis movable along the length of the bridge, thereby eliminating thenecessity for repeatedly dismantling and reconstructing the trafficshield as the maintenance, repair or construction operations on thebridge continue progressively along the length of the bridge, the safetytunnel riding on rails, and the safety tunnel being alternately lockedand unlocked on the rails, wherein the safety tunnel has an interiorwidth which is equal to or greater than the usable given width of theroadway thereby minimizing any interference with the normal traffic flowon the bridge, and wherein the roadway of the bridge has respectivesides, each of which is provided with a parapet, wherein the rails aremounted on the parapets, and wherein the movable safety tunnel rides onthe rails on the parapets.
 2. The improvement of claim 1, wherein thesafety tunnel has a trolley system riding on the rails.
 3. Theimprovement of claim 2, wherein the trolley system is locked to arespective longitudinal section of the rails as the maintenance, repairor construction operations are being performed on a correspondingrespective length of the bridge.
 4. The improvement of claim 3, whereinthe trolley system is unlocked from the respective longitudinal sectionof the rails to enable the safety tunnel to be moved to the nextadjacent section of the bridge on which the maintenance, repair orconstruction operations are to be performed.
 5. The improvement of claim4, wherein the safety tunnel is pushed and/or pulled to the nextadjacent section of the bridge.
 6. The improvement of claim 2, whereinthe trolley system comprises a plurality of respective spaced-aparttrolley assemblies.
 7. The improvement of claim 6, wherein the safetytunnel comprises an inverted U-shaped structure having a roof assemblyjoined to respective sides depending therefrom, and wherein therespective sides have lower portions carried by the plurality of trolleyassemblies riding on the respective rails.
 8. In a bridge having aroadway for vehicular and/or pedestrian traffic, the roadway having ausable given width for normal traffic flow, wherein the roadway hasrespective sides provided with parapets, and wherein maintenance, repairor construction operations are being performed on the bridge, a movablesafety tunnel within a respective longitudinal section of the bridge,thereby enabling the traffic to flow on the roadway of the bridgesubstantially uninterrupted while the maintenance, repair orconstruction operations are being performed on the respectivelongitudinal section of the bridge, such that the traffic on the roadwayof the bridge is protected against falling debris, the tunnel comprisingan inverted U-shaped structure including a roof having respective sidesdepending therefrom, the sides having lower portions provided with atrolley system riding on rails on top of the respective parapets,wherein the trolley system is locked to a respective longitudinalsection of the rails as the maintenance, repair or constructionoperations are performed on a corresponding respective length of thebridge, and wherein the trolley system is unlocked from the respectivelongitudinal section of the rails to enable the tunnel to be moved tothe next adjacent section of the bridge on which the maintenance, repairor construction operations are to be performed and wherein the safetytunnel has an interior width which is equal to or greater than theusable given width of the roadway, thereby minimizing any interferencewith the normal traffic flow on the bridge.
 9. The improvement of claim8, wherein the trolley system comprises a plurality of respectivespaced-apart trolley assemblies.
 10. In a bridge having a roadway forvehicular and/or pedestrian traffic, wherein the roadway has respectivesides provided with parapets, and wherein maintenance, repair orconstruction operations are being performed on the bridge, a movablesafety tunnel within a respective longitudinal section of the bridge,thereby enabling the traffic to flow on the roadway of the bridgesubstantially uninterrupted while the maintenance, repair orconstruction operations are being performed on the respectivelongitudinal section of the bridge, such that the traffic on the roadwayof the bridge is protected against falling debris, the tunnel comprisingan inverted U-shaped structure including a roof having respective sidesdepending therefrom, the sides having lower portions provided with atrolley system riding on rails on top of the respective parapets,wherein the trolley system is locked to a respective longitudinalsection of the rails as the maintenance, repair or constructionoperations are performed on a corresponding respective length of thebridge, and wherein the trolley system is unlocked from the respectivelongitudinal section of the rails to enable the tunnel to be moved tothe next adjacent section of the bridge on which the maintenance, repairor construction operations are to be performed, wherein the trolleysystem comprises a plurality of respective spaced-apart trolleyassemblies, and wherein each trolley assembly comprises a wheelrotatably journaled in bearings carried by respective spaced-apartchannels, and a plate on each side of the wheel, the plates straddlingthe rail.
 11. The movable safety tunnel of claim 10, wherein the railcomprises a closed channel rail.
 12. The movable safety tunnel of claim10, wherein each trolley assembly carries J-bolts, one on each sidethereof, the J-bolts having respective nuts and further havingright-angularly bent portions received below the respective rails,thereby locking the J-bolts to the rails, such that the nuts on theJ-bolts may be loosened, and such that the J-bolts may be turnedsubstantially 180° to clear the rails, thereby unlocking the trolleyassemblies and assembling the movable safety tunnel to be moved into itsnext position along the bridge.
 13. In a bridge having a roadway forvehicular and/or pedestrian traffic, wherein the roadway has respectivesides provided with parapets, and wherein maintenance, repair orconstruction operations are being performed on the bridge, a movablesafety tunnel within a respective longitudinal section of the bridge,thereby enabling the traffic to flow on the roadway of the bridgesubstantially uninterrupted while the maintenance, repair orconstruction operations are being performed on the respectivelongitudinal section of the bridge, such that the traffic on the roadwayof the bridge is protected against falling debris, the tunnel comprisingan inverted U-shaped structure including a roof having respective sidesdepending therefrom, the sides having lower portions provided with atrolley system riding on rails on top of the respective parapets,wherein the trolley system is locked to a respective longitudinalsection of the rails as the maintenance, repair or constructionoperations are performed on a corresponding respective length of thebridge, and wherein the trolley system is unlocked from the respectivelongitudinal section of the rails to enable the tunnel to be moved tothe next adjacent section of the bridge on which the maintenance, repairor construction operations are to be performed, wherein the trolleysystem comprises a plurality of respective spaced-apart trolleyassemblies, and wherein the trolley assembly includes a gusset assemblyhaving a pair of spaced-apart upwardly-extending gusset plates, andwherein a column has a lower portion secured between the gusset plates.14. The movable safety tunnel of claim 13, wherein the column has anupper portion, and wherein the roof of the tunnel has depending memberstelescoped within the upper portion of the column and secured thereto.15. The movable safety tunnel of claim 14, wherein the depending membersof the roof are adjustable vertically with respect to the columns. 16.The movable safety tunnel of claim 13, wherein the sides of the movablesafety tunnel comprise a plurality of side panels secured betweenrespective columns.
 17. In the method of maintaining a bridge, theimprovement wherein the traffic may flow along the bridge or under thebridge while the maintenance is being performed on the bridge, thebridge including a roadway having a usable given width for normaltraffic flow, comprising the steps of providing a movable safety tunnel,the tunnel including a plurality of individual sections coupled end toend, and moving the safety tunnel along the bridge as the maintenance onthe bridge progresses along the length of the bridge, the tunnel havingan interior lateral width which is equal to or greater than the usablegiven width of the roadway, thereby minimizing any restriction orinterference with the normal traffic flow on the bridge, wherein themovable safety tunnel comprises an inverted U-shaped structure whichcooperates with the roadway to form an enclosure for the traffic flow,wherein the roadway of the bridge has respective parapets, and whereinthe movable safety tunnel rides on the parapets.
 18. The method ofclaims 17, further comprising the step of securing rails on therespective parapets, and wherein the movable safety tunnel has a trolleysystem that rides on the rails on the respective parapets.
 19. In atunnel intended to maintain traffic flow on a bridge during maintenanceor repair operations on the bridge, wherein an outer shroud or envelopeis constructed externally of the tunnel to confine any dust particles ordebris and thus eliminate inadvertent environmental pollution, andwherein the bridge has a roadbed having a usable given width for normaltraffic flow as defined by parapets or barriers on each side of theroadbed, the improvement comprising trolley assemblies carrying thetunnel and riding on rails on the parapets, wherein the trolleyassemblies may be selectively locked and unlocked from the rails, andwherein the rails as well as the tunnel and the trolley assembliescarrying the tunnel have an interior lateral width therebetween which isequal to or greater than the usable given width of the roadbed, therebyminimizing any restriction or interference with the normal traffic flowon the bridge during maintenance or repair operations thereon.
 20. Theimprovement of claim 19, wherein the tunnel comprises a plurality ofindividual sections coupled together.
 21. The improvement of claim 20,wherein the tunnel includes a roof having an adjustable height.
 22. In atunnel intended to maintain traffic flow on a bridge during maintenanceor repair operations on the bridge, wherein an outer shroud or envelopeis constructed externally of the tunnel to confine any dust particles ordebris and thus eliminate inadvertent environmental pollution, andwherein the bridge has a roadbed having a usable given width for normaltraffic flow, the improvement comprising trolley assemblies carrying thetunnel for movement longitudinally of the bridge, the trolley assembliesbeing selectively locked and unlocked with respect to the bridge, thetunnel and the trolley assemblies having an interior lateral widththerebetween which is equal to or greater than the usable given width ofthe roadbed, thereby minimizing any restriction or interference with thenormal traffic flow on the bridge during maintenance or repairoperations thereon, the tunnel including a plurality of individualsections coupled together end to end, wherein parapets are provided ateach side of the roadbed, and wherein rails are mounted on top of theparapets, the trolley assemblies riding on the rails.
 23. In a tunnelintended to maintain vehicular traffic flow on a bridge duringmaintenance or repair operations on the bridge, wherein an outer shroudor envelope is constructed externally of the tunnel to confine any dustparticles or debris and thus eliminate inadvertent environmentalpollution, and wherein the bridge has a roadbed defined by parapets oneach side of the roadbed, the parapets having respective top surfaces,the improvement comprising trolley assemblies riding on respective railson the parapets, each rail comprising a closed tube having asubstantially square hollow cross-section construction including upperand lower walls, the top wall having an access hole formed therein, andthe lower wall being secured to the top of the respective parapetthrough the access hole in the top wall.
 24. The improvement of claim23, wherein a hole is formed in the lower wall along the longitudinalcenter line of the rail, and wherein a concrete anchor passes throughthe hole in the lower wall and into the parapet.
 25. The improvement ofclaim 23, wherein the roadbed as defined by the respective parapets hasa usable given width; and wherein the rails, and the tunnel with thetrolley assemblies riding on the rails, have a lateral interior widthwhich is equal to or greater than the usable given width of the roadbed.